We are testing the hypothesis that Streptococcus mutans is responsible for a measurable amount of decay in humans. Rampant caries individuals, i.e. individuals with less than or equal to 10 carious teeth, have high levels of Strep mutans in their plaque. We are making a bacteriological diagnosis of Strep mutans infection and treating these individuals topically with either 5 percent Kanamycin or 1.23 percent NaF in a pleasant tasting gel. The subjects are treated twice a day for a one week period on two occasions, i.e. prior to the placement of dental restorations and immediately after the placement of the restorations. Fissure, and proximal plaque samples and saliva are cultured before and after each treatment period and at the recall periods for total viable counts, Strep mutans and Strep sanguis counts. A placebo group is included. Subjects are randomly assigned to the treatment groups. The clinical scoring of caries and the bacteriological analysis are performed in a double blind procedure.